Discussion on the formation and prevention of neps

Foreword

A neps are micro-aggregates in which fibers are polymerized into knots due to improper processing of raw materials, spinning processes, or spinning processes. It generally cannot be pulled apart by hand. Cotton fiber and chemical fiber can form a neps, but the probability of chemical fiber formation is low. The neps and impurities in the spinning are different, and the two can not be confused, but have certain relevance. This paper mainly discusses the formation and prevention of neps in raw cotton.

1, the danger of nep

Neps and impurities are the main defects of yarn formation, which directly affect the appearance and quality of yarns and post-processed products, and have a considerable impact on the production of post-processing. The impurities of the yarn are removed in the post-processing winding process and the dyeing and finishing process, such as clearing on the winder, scouring of the dyeing and finishing process, and brushing of the fabric, which can usually be partially or largely removed; The chance of removal of the neps in the subsequent process is low. Most nep will form obvious small black spots or thick knots in printing and dyeing fabrics; the neps formed by immature fibers often form "white stars" in the dark and special dark fabrics, causing the color difference and color of the fabric. Even caused a quality compensation accident. The relevant information shows that 27.9% of the large seeded neps can cause the yarn to break. Large neps can also interfere with the normal drafting of the spun yarn. Therefore, cotton mills must list cotton knots as the main daily work, and controlling cotton knots is an eternal issue for mills. The number of neps of 1 g cotton yarn is one of the technical conditions for cotton yarn evaluation.

2, classification of neps

2.1 Classification by nep color

Generally, the neps are either natural or white, but also yellow, gray, light red, and black due to poor cotton color, mildew, insect secretion, and staining.

2.2 Classification by nep shape

Generally, the neps are round, but also have a sheet shape and a flat shape as well as a bundle of filaments. Spherical neps are often referred to as cotton granules and are often formed by a combination of a spinning frame and a wire ring.

2.3 According to whether the neps are classified as adhesion impurities

Many neps have seed or seed shells, which are connected to each other and are said to have a seed lint. Figure 1 shows a general nep, and Figure 2 shows a tamp with a seed. The seed lint accounts for about 10% of the total number of neps. Because it is adhered to the yarn, it is very harmful and is the most harmful defect of raw cotton.

2.4 Classification by fiber maturity in nep

The neps can be composed of a mixture of normal mature fibers, immature fibers, and dead cotton fibers. The neps containing immature fibers and dead fibers are extremely harmful.

2.5 by cotton knot loose, tight classification

Generally, it can be divided into loose cotton knots and tight cotton knots, but it is difficult to quantitatively distinguish them. Obviously, tight cotton knots are more harmful than loose cotton knots.

2.6 sorted by nep size

Uster strip uniformity meter lists the cotton knot as a regular defect, and the average diameter (μm) is greater than the original yarn +140%, the length is 1mm as the reference length, and the nep is divided into +140%. +200%, +280%, +400% four gears to distinguish the size of the neps (including the neps with seed chips). The effect of nep size is related to the density of the spun yarn, and the smaller the line density, the higher the sensitivity to the neps size. Uster MN100 type nep process control system can determine the number and size of neps, and propose the critical point of the average neps size control of different yarn counts, as shown in Figure 3, for reference. The black dot in the figure is the critical control value of the AFIS neps size of 9.84 tex (60Ne).

Large neps can cause the rear process to block the cotton collector and the yarn guide, causing breakage or yarn defects, which is more harmful than a small cotton knot.

3, nep detection

The traditional method for testing cotton neps and impurities has been eliminated. At present, the cotton sliver is usually drawn into a cotton net or a simple drafting device is used to draw into a cotton wool, and the neps and impurities are visually observed on a tester equipped with a light source. At present, the instrument test has matured, and its sample quantity is large, and the test efficiency is high, which can solve the visual difference between people.

The main instruments for testing neps impurities are as follows:

(1) AFIS single fiber test system

It can quickly, conveniently and correctly test the knots, impurities and fiber length, maturity and other indicators of raw cotton, sliver and roving; the test data can be compared with Uster statistics. The Uster AFIS neps impurity detection method is approved by ASTM and ITMF.

The XJ129 type and the Indian Premier aQura type neps and short fiber tester of Changling, Shaanxi, China are basically the same as the AFIS instrument.

(2) YG091 type neps impurity tester and NATI neps impurity tester are basically the same in structure and principle. It divides the neps into three categories: ≥0.5mm, ≥0.7mm, ≥1mm.

(3) Uster720 type nep tester

It is an option for the Uster HVI High Capacity Tester and can be used alone to measure the neps of raw cotton, raw strips and combed strips. It is a UsterLVI low volume instrument. The ginning mill and textile mill can be used conveniently.

(4) Uster MN100 type nep process control system

It is based on the AFIS standard test and can accurately test the number and size of neps. The test range is from raw material to roving. The control chart and the critical size of the neps are provided. Compared with the Usterster statistical bulletin, it becomes the source of monitoring neps, product quality control, Tools for decision making, such as equipment maintenance and process design.

According to the relevant literature, visual inspection of cotton neps is significantly correlated with AFIS test neps and NATI test neps; this proves that the instrument test has matured and is recognized by the public.

(5) On-line detection of neps and impurities

Online detection is the ideal solution for connecting detection, control, adjustment and analysis. Trüctzschler TC03 type carding machine is placed under the doffer and under the stripping roller. The electronic camera scanning sensor along the width of the doffer can detect the size and quantity of neps and impurities. The test results are processed, displayed and printed by computer. Understand the dynamics of neps impurities, monitor raw materials and production operations.

4. Changes in the neps of the spinning process

After the cotton is made of cotton, the cotton knot has a large increase. Cards and combers can significantly reduce the neps. From the combed strip to the roving, there is no big change in the neps, and the weight of the neps is reduced in the three processes of opening the cotton, combing and combing.

The general rule of the knots of each machine in the open cleaning process is shown in Figure 5. It indicates that the raw cotton is grasped, opened, mixed, and cleared to the cotton, and the neps are gradually increased, and the rising slope of the raw cotton to the clean cotton is large.

The change in the neps of a card tampon can be summarized as follows:

In the formula S=B+C+-C-, S is the number of neps per gram of raw strips; C+ is the number of neps per gram produced by the carding; C- is the number of neps per gram of combing and excluding.

Requires S < span="">, must be C-> C+ <> Some people think that during the drawing process, it is possible to draw the fibers with poor resolution and parallelism into neps, and the neps will be significant. Increased, the author believes that there seems to be a lack of strong scientific evidence.

5, the main reason for the formation of neps

The neps are made up of fibers twisted into a mass, the main reasons are as follows.

(1) Immature fibers have poor elasticity, low rigidity, strong hygroscopicity, and are easily kinked into a neps.

(2) The cotton wool, the hard seed epidermis, the insect cotton, the sugar-containing cotton, etc. in the seed cotton are easily formed into a neps by being struck and dispersed.

(3) Seed cotton and broken seeds are easily hit by fiber-seed lint.

(4) The ginning and opening of the cleaning cotton are not good, and the rolling brake will form a bundle of yarns, wherein the combed cotton can not be combed into a single fiber state, and a cotton knot will be formed.

(5) Poor fiber transfer between the carding elements may cause excessive combing or even formation of returning flowers, resulting in neps.

(6) The spacing of the carding elements is too large, the combing is insufficient, and the neps are easily formed. Repeated combing of free fibers between components also increases the neps.

(7) The carding elements are not sharp or burr, missing teeth, not smooth, and the entangled fibers are repeatedly over-combed to form a neps.

(8) The cotton fiber is damp or the moisture regain is too high, and the fiber is easy to agglomerate and entangle to cause a neps.

(9) The spacing of the carding components is too small, the component speed is too high, the striking or combing force is too large, resulting in fiber damage, increased lint, and increased neps.

(10) Fibers with small fineness and long length, soft fibers are easily kinked and entangled to form neps, such as long-staple cotton, fine denier, and ultra-fine fibers.

6. Countermeasures for controlling neps

6.1 raw cotton

The main factors affecting the neps are the maturity, fineness, short-staple rate, soft-skin epidermis, and soft-skinned spots of the original cotton, which are all significantly correlated with the neps. The maturity is closely related to the fineness itself. The relationship between maturity coefficient and nep is shown in Figure 6. High maturity, good fiber strength, natural curling, good rigidity, good elasticity, low hygroscopicity, and the possibility of being rubbed and entangled to form a neps during opening, striking, and combing. In view of this, the focus of reducing the neps is to control the maturity of the raw cotton. For grades with higher requirements for neps, the maturity factor should be in the range of 1.55 to 1.75.

The content of soft seed skin and stiff cotton in raw cotton directly affects the amount of white stars in the dyed cloth, which should generally be less than 0.5% of the total amount of the spot.

The number of cotton knots in the recycled and reused cotton is several tens of times higher than that of the original cotton. It should be controlled according to the variety requirements. The high-end products should be deactivated, and then the cotton should be treated before reuse.

6.2 ginning

The rolling of cotton has two types of leather roller and serrated cotton. The cotton roller gin is relatively gentle, with less damage to the fiber, less neps and bundles; but there is no waste device, more dead cotton, soft seed skin, etc., low yield and high production rate, including short pile rate Also higher.

The sawtooth cotton strike is more severe, which is easy to damage the fiber and the bundle of silk and cotton knots. It is especially easy to form a hook-shaped cotton bundle; the impurity content is low, but it is easy to form fiber-breaking seeds or seed chips. The low velvet rate is low, which is good for the strip.

Due to the low production of the skin ginning, in addition to raw cotton such as long-staple cotton, which has high requirements on the quality of the neps, serrated cotton is generally used.

The temperature and humidity of the ginning process and the rolling process have a great relationship with the formation of neps and bundles. The ginners should strictly control the moisture regain of raw cotton and the preferred production process parameters.

6.3 open cotton

6.3.1 Configuration of the cleaning cotton process unit

The traditional point of view emphasizes improving the efficiency of removing impurities and reducing the impurity content of cotton quilts (ç­µ cotton), and the latter is the main indicator of the quality of cotton cleaning, which leads to an increase in the number of open cotton blows, and the attack speed is too fast, resulting in an increase in the number of filaments. The neps are increased and the impurity splitting becomes smaller and more. The configuration mode of the modern open cleaning unit: the general raw cotton can be configured with a process of grasping, opening and mixing; the long-staple cotton and chemical fiber can be configured with a short process mode of one catching, one mixing and one clearing; Ring spinning and general rotor spinning with a cotton yarn and raw cotton content of more than 3.0% can add a clean cotton. The reduction of the cleaning unit is conducive to the reduction of neps, bundles and short piles. Rieter's data shows that when processing Tencel microfibers, the card can reduce the knot by 80% when using a hit point. If you increase the opening point, the neps will increase by about 20%.

6.3.2 Optimization of opening and cleaning machine

There are different forms of opening and cleaning cotton, and the types of hitting hands are different. The impact force, the impact impulse, the puncture ability, the opening and the removal efficiency are all different. It is generally believed that the sheet-shaped beater has a large impact, and the opening is severe, with edges and edges, and the edges and corners are easy to damage the fibers, break the impurities, and produce a bundle of yarns which are unfavorable to the neps. Corner nails or comb needles, strong puncture ability, easy to penetrate into the fiber layer, no edges and edges, not easy to damage the fiber. The smaller shape of the comb needle nail hitch has a carding effect and is suitable for the cotton cleaner. The sawtooth hitter hits the middle of the punch, it is better to open a small cotton block, but there are edges, edges and corners, easy to damage the fiber, crushing impurities; the treated fiber is easy to be embedded in the root, and the cotton knot is formed after winding.

According to the relevant test data, the needles and the cotton knots and the short velvet are the least, the nose-shaped beaters are the second, and the serrated beaters are the most. The cleaning process is due to the fact that the fibers are still in a small cotton lump condition, and the serrated beating should be used with caution. Chemical fiber, long-staple cotton, fine-denier fiber should be beaten with a needle.

It is generally believed that the free strike force is small; the grip is large, and it is easy to damage the fibers, produce neps and impurities. Therefore, it is advisable to use free blows to catch cotton and open cotton, and to use combs for holding cotton. Therefore, the porcupine-type opener that uses the grip is gradually replaced by the axial-flow opener that the airflow conveys freely.

6.3.3 Speed ​​of opening and clearing components for cleaning machine

The process of opening and cleaning cotton should follow the principle of gradually opening and accelerating step by step. The fiber flow should be smooth, prevent returning flowers or repeatedly rolling between adjacent parts, resulting in repeated blows and increased neps; equipment connection output should be balanced and operated. The rate is over 90%. Avoid violent snagging and friction of the fibers and the striking parts to entangle the fibers into bundles, resulting in neps and bundles. Pay attention to the neps formed by the repeated rolling of the mechanical fibers of the cotton box. According to the information, the cotton box machinery is twice as high as the axial flow opener.

In addition, the outside of the beater should be appropriate to prevent the beater from winding around and increase the end of the cotton. It is necessary to prevent traffic jams and rolling brakes. The parts and passages should be smooth, prevent sticking, and repeatedly strike to form bundles.

6.4 Production and prevention of neps in the carding process

The main function of the card is to comb the fibers into a single fiber state, combing most of the neps and bundles formed by the open cotton, and eliminating the bundles and neps. Therefore, the total neps should be reduced, but improper handling will also increase the neps.

6.4.1 Adopting a strong combing process route

Under the condition that the carding machine is in good condition, under the condition of sharp and smooth combing components, the reinforcing combing can reduce the neps, and the strong combing mainly adopts the high speed of the cylinder, in the licking roller~the cotton board, the cylinder~cover The tight spacing is used between the cylinders of the cylinders, the licking rollers and the carding plates to improve the combing ability and reduce the returning flower to increase the fiber transfer rate, but it is necessary to prevent excessive combing and damage the fibers. The distance between the long-staple cotton, chemical fiber, and fine-denier fiber should not be too small, and it is necessary to prevent the surrounding forest from being formed by the small distance between the cylinder and the cover. At the same time, the pre-carding original can be added to enhance the carding effect.

6.4.2 Preferred carding elements

Depending on the spinning fiber, the density of the spun yarn, and the yield of the card, the type of the squeegee and the clothing are preferred, and will not be described here.

6.4.3 From the low setting of the licker speed to ensure good fiber transfer

The speed of the licking roller affects the strength of the holding card and the transfer of the fiber to the cylinder, which has a great relationship with the formation of fiber damage and neps.

When the sliver weight is 23.8g/5m and the card output line speed is 119m/min, the relationship between the speed of the licker and the sliver is shown in Table 1.

It can be seen that the low speed and high speed of the licker roller are unfavorable to the neps. The relevant research results indicate that the transfer coefficient of metal card clothing is only 0.2~0.3, which means that one fiber can be transferred to Doffer by 3~5 turns of cylinder. Therefore, increasing the speed ratio of the cylinder to the licker roller can increase the transfer rate of the licker roll and prevent the returning flower from rubbing into a knot. The speed ratio of the high-yield card should be more than 2 times. The spiny roller and the licking roller have high rotation speed and are easy to produce neps, which should be used with caution.

6.4.4 Reducing the knots of fiber entanglement and returning flowers

The cylinder cover combing is free combing. If the needle teeth are burred, crushed, inverted, and rusted, the fibers will be embedded, hung, wrapped, and twisted to form a flower, and the neps are repeatedly combed. To achieve the thorn thorn roll, cover cotton net cleaner without burrs, sharp, smooth.

6.4.5 Elimination of fortified knots

The cover plate has special functions for eliminating the cotton knots with fiber seed chips and fiber soft seed skin. When the cotton knots are more, the speed of the cover plate should be accelerated, and the front and rear fixed cover plates, the cotton net cleaner and the spinner roller pre-separated comb are used as much as possible. The board removes the effect of the neps. The licker part should be excluded from the seeds, stiff cotton and fine impurities as much as possible.

6.5 Production and prevention of neps in the combing process

6.5.1 Relationship between combing preparation and neps

The influence of the combing preparation process on the neps can not be ignored. The pre-adhesive-strip-rolling process fiber has high degree of separation and parallelism, which can reduce the cotton loss and eliminate the short velvet and neps, but it is easy to stick, and the total combination number and total drafting multiple must be controlled accordingly.

6.5.2 Cotton drop rate and combed neps

The combed cotton can eliminate the neps and lint in the sliver in large quantities. The combing rate should be comprehensively determined according to the product quality requirements, the density of the spun yarn, the user's needs and the cost of the product. The rate of cotton drop can also be used as a means of controlling the neps, and is adjusted in time according to objective changes such as changes in raw materials.

6.5.3 Pay attention to the specifications, quality, top comb and brush status of the cylinder.

In addition to carding gauge, positioning, timing, cylinder specifications, sharpness, finish, top comb specifications and status, brush quality are directly related to the removal of neps. It should be paid attention to and preferred.

7. Reference indicators for process neps

7.1 The rate of increase and decrease of cotton, carding and combed neps:

The rate of increase and decrease of open cotton, carding and combed neps is ≤+80%, ≥-80%, ≥-20%.

8, the conclusion

(1) The neps are very harmful to the spinning and post-processing products, especially the neps with seed chips; the neps with low mature fibers and the large neps and tight neps. The impurities in the fabric are scoured and brushed, and more than 50% can be removed. Spinning should focus on reducing neps.

(2) The reduction of neps should start from the raw materials, and the key points should be to control the micronaire value and the maturity of the raw cotton and the rolling mill and the short pile rate. For high-end products, it is recommended to use raw cotton with a good maturity of 1~3, containing cotton knots and less bundles, and using a combing process. The recycled cotton, the combed cotton, the cover flower, and the like, the cotton contains a large amount of cotton knots and short velvet, and is only suitable for medium and low-grade products such as medium and thick yarns. The high moisture regain of the fiber is easy to produce neps, and the ginning and combing workshop should control the low relative humidity.

(3) The cleaning process should focus on reducing the production of neps and bundles and short piles. The carding process should focus on the combing of the neps, the elimination of the neps and the prevention of the formation of the neps. The combing process should be based on the removal of short piles.

(4) The control of neps involves the comprehensive management of raw materials, processes, equipment and equipment, management and environment.

Author: XXX; Source: China Network yarn; agricultural futures to reproduce this network to disseminate more information purposes only, does not mean Ben Wang approved the text of the opinion. If the author of the reprinted article believes that there is something wrong with this website, please contact us at 010-51289506. This website will immediately negotiate with you and resolve related matters.

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Article Keywords: Agricultural Products Futures Cotton

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